Is solar-induced chlorophyll fluorescence derived index much useful in agricultural drought monitoring

Drought is multifaceted, more frequent hydrometeorological phenomena occurring worldwide. The intensity and frequency of droughts are increased with rising trend of global warming. These events significantly impact society which directly linked to agricultural productivity and economy. India witnessed these extreme drought events and have faced serious economic loses. Therefore, more effective, and reliable drought monitoring is essential for its mitigation and to enhance early warning systems. In addition, there are limited studies looking at the sensitivity of solar-induced chlorophyll fluorescence (SIF) to response of meteorological parameters during drought event.   

Therefore, a maiden attempt is taken to understand how terrestrial vegetation response under severe drought event which experienced in 2009 summer monsoon period (June to September) over Indo-Gangetic plain regions in India. We studied the productivity of vegetation over IGP region using solar-induced fluorescence as a proxy. Moreover, we have derived drought indices herein Standardized Precipitation Evapotranspiration Index (SPEI), Standardized Soil Moisture Index (SSI), and SIF Health Index (SHI). These indices were utilized gridded monthly precipitation, evapotranspiration, soil-moisture, land surface temperature (LST) and solar-induced fluorescence (SIF) datasets from 2001 to 2020 over IGP region. In addition, statistical relationships and trends among these indices are evaluated through the Pearson correlation coefficient and Mann-Kendall test.

Our findings provide promising results by addressing the major drought events over Indo-Gangetic plains in India in terms of intensity and spatial coverage. There is great significance to further understand the application of SIF in agriculture drought detection. The spatio-temporal patterns and trends of standardized precipitation evapotranspiration index (SPEI), and standardized soil-moisture index (SSI), have compared against solar-induced chlorophyll fluorescence health index (SHI) anomaly for short, and mid-term (herein 01, 03 and 06 month time scales) for seasonal drought monitoring. Furthermore, the spatial extent of SPEI, SSI and SHI anomaly well agreed for the 2009 drought event across region.

Overall, SIF can be reliable tool for agricultural drought monitoring in a timely and accurate manner. The resultant water stress leads to reduction in vegetation which reflected changes in SHI anomaly. This showcasing the ability of SIF to provide insight the link between carbon and water during droughts. Furthermore, it will enhance information for stakeholders, interested into future carbon-water cycle studies.

 Keywords: SPEI, SSI, SHI, and agricultural drought.